Apparatus for controlling environmental conditions, especially suitable for use underwater

ABSTRACT

The disclosure illustrates a self-contained closed circuit type underwater breathing apparatus for diver use. A plurality of three or more oxygen sensor cells, each thermistor temperature compensated, are exposed to the gas stream in the system, each providing a current resulting in voltage drop across the thermistor, directly related to oxygen concentration, which voltages then are electronically processed to operate oxygen supply means, whereby oxygen partial pressure is maintained within a predetermined range. In the processing, amplified signal voltages are electronically mathematically averaged and processed to deliver a single control signal to an oxygen solenoid valve. The system is adjusted at atmospheric pressure to provide one half atmosphere oxygen partial pressure at a selected voltage level, e.g., about 2.4 volts average amplified cell voltage. As the quantity of oxygen thereafter varies in use by the diver, the average voltage varies linearly and the solenoid acts responsively thereto. Each amplified cell output is also connected into separate alarm and visual indicator circuitry so that should any cell provide a voltage corresponding to oxygen partial pressure below or above a predetermined safe oxygen range, an audible alarm is sounded and the diver may observe the individual indicators provided for each of the sensor cells and, thereupon, determine emergency remedial steps. Normally, the diver will presume any two similar partial pressure indicators to be correct. The design of the system is such that the electronic circuitry responds to limit, or stabilize, the effect of a spurious voltage input upon the average voltage via transistor clipping circuitry and an associated regulated voltage source. Thereupon a non-varying voltage, which is not outside the selected saft range constantly appears in the average voltage. Accordingly, the new effective average voltage continues effectively to maintain a suitable oxygen partial pressure as long as the signals from the remaining cells themselves are a correct measure of the oxygen partial pressure actually in the system.

United States Patent 1 Kanwisher et al.

[111 3,727,626 [45] Apr. 17,1973

( [22] Filed:

[ APPARATUS FOR CONTROLLING Y ENVIRONMENTAL CONDITIONS,

ESPECIALLY SUITABLE FOR USE UNDERWATER Nov. 4, 1970 [21] App]. No.:86,991

Related U.S. Application Data [62] Division of Ser. No. 780,961, Dec. 4,1968, Pat. No.

PrimaryExaminer-Alan Cohan Assistant ExaminerDavid J. Zob kiwAttorney-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT The disclosureillustrates a self-contained closed circuit type underwater breathingapparatus for diver use. A plurality of three or more oxygen sensorcells, 7

each thermistor temperature compensated, are exposed to the gas streamin the system, each providing a current resulting in voltage drop acrossthe thermistor, directly related to oxygen concentration, which voltagesthen are electronically processed to operate oxygen supply means,whereby oxygen partial pressure is maintained within a predeterminedrange. In the processing, amplified signal voltages are electronicallymathematically averaged and processed to deliver a single control signalto an oxygen solenoid valve. The system is adjusted at atmosphericpressure to provide one half atmosphere oxygen partial pressure at aselected voltage level, e.g., about 2.4 volts average amplified cellvoltage. As the quantity of oxygen thereafter varies in use by thediver, the average voltage varies linearly and the solenoid actsresponsively thereto. Each amplified cell output is also connected intoseparate alarm and visual indicator circuitry so that should any cellprovide a voltage corresponding to oxygen partial pressure below orabove a predetermined safe oxygen range, an audible alarm is sounded andthe diver may observe the individual indicators provided for each of thesensor cells and, thereupon, determine emergency remedial steps.Normally, the diver will presume any two similar partial pressureindicators to be correct. The design of the system is such that theelectronic circuitry responds to limit, or stabilize, the effect of aspurious voltage input upon the average voltage via transistor clippingcircuitry and an associated regulated voltage source. Thereupon anon-varying voltage, which is not outside the selected saft rangeconstantly appears in the average voltage. Accordingly, the neweffective average voltage continues effectively to maintain a suitableoxygen partial pressure as long as the signals from the remaining cellsthemselves are a correct measure of the oxygen partial pressure actuallyin the system.

24 Claims, 4 Drawing Figures AUIDIBLE ALARM PATENTEB AFR] 71975 SHEET 1[IF 3 PATENTEDAPR] 71975 sum 2 UF 3 FIG.2

OXYGEN FROM PRESSURE ATOR VALVE-44 FROM 54 MOUTH PIECE-2O APPARATUS FORCONTROLLING ENVIRONMENTAL CONDITIONS, ESPECIALLY SUITABLE FOR USEUNDERWATER This invention relates to apparatus and methods formaintaining a safely breathable atmosphere, and most especially so underconditions which are not normal to human life. The invention isparticularly advantageous in the underwater environment, such as inmaintaining a constantly safe oxygen level in deep sea chambers anddiver breathing equipment. Broadly considered, however, the inventionfinds application also in space apparatus and, as will appear, ininstance under ordinary atmospheric pressure conditions. Further,although the invention is especially advantageously applicable to theprotection of human life, it is applicable in the maintenance of asuitable atmosphere or other critical condition regardless of the objectof protection or the condition desired to be maintained.

The invention in structure and modes of operation is exemplified hereinby illustrating and describing underwater breathing apparatus of theself-contained closed circuit type, recently, and now more prominently,coming into use by divers. The invention is especially useful forrelatively deep diving but it is equally adapted for shallow water.

Generally described, and as revealed by the prior art. the closedcircuit type of diving equipment involves inhalation and exhalationwithin the confines of the equipment. Thus, normally none of the gasesare discharged from the equipment except on ascent, when it is necessaryto release internal pressure. Known units, such as shown in U.S. Pat.No. 3,252,458, include a carbon dioxide absorber thru which the gasatmosphere is passed on inhalation or exhalation, the oxygen level beingconstantly monitored and replenished up to a predetermined level. Aswill be understood, therefore, this type of system is highly desirablebecause no oxygen is wasted on exhalation, and the diluent gas, usually(costly) helium in deep water, is completely conserved. Consequently.longer period underwater ventures are readily feasible and at very greatsaving in cost of helium.

The aforementioned U.S. Pat. No. 3,252,458 is believed to constitute themost closely allied description of apparatus relative to the presentinvention.

described as a polarographic cell. The cell is positioned in the gasstream for contact therewith following the carbon dioxide eliminationstage. The cell operates to deliver a minute electric signal varyingwith the concentration of oxygen in the stream, oxygen actuallypentetrating into the cell and effecting a flow of current according toits partial pressure. The electric signal thus developed is utilized byassociated electric circuitry to operate oxygen input means whereby thediver is supplied with additional oxygen from the oxygen tank as needed.

The aforesaid U.S. Pat. No. 3,252,458 constitutes a substantial advancein the art of underwater breathing. As is well known to those involvedin this art, the ventures of divers involve extreme dangers to life; andeven where death may be avoided, serious physiological impairment mayresult during a necessary but too rapid decompression. The aforesaidpolarized cell, being an extremely rapid responder to oxygen, andaffording thereupon a constant and reliable output signal, has

rendered breathing apparatus of the type under consideration far morefeasible. However, the hazards are 5 so great as to command the greatestpossible degree of certainty of continuously perfect suitability to theneeds of the diver as they suddenly develop underwater; otherwiseunderwater technological advances will be seriously hampered by refusalof people to work in the art. In other words, practicalities considered,the ultimate in possible safety is needed. To this end, quality incomponent parts is essential and it is of prime importance that theentire system function properly as an assembly. Even though such beprovided, failures in any equipment must be recognized as inevitable.

Serious failures are minimized to an extremely high degree by thepresent invention and such as may possibly occur in using this inventionare reduced to a level of substantially zero criticality. This is incontrast to the prior levels of achievement of other workers whichleaves much to be desired. As aforesaid the teaching of the prior artare notable and it is not intended unduly to speak disparagingly ofthem. How ever, the prior art stopped seriously short of the desirableunderwater safety standards in a number of respects, and it must bepointed out that the known teachings and equipment expose the diver toextremely dangerous conditions in the event of a particular type ofelectronic and/or associated equipment failure. Unfortunately suchequipment failure is inherently possible and quite likely to occurespecially in the course of use of equipment over a long period of time.This particular fault will be described more fully in relation to thepresent invention; however, a few brief comments at this point willserve to bring the matter to sharp focus absent surrounding shroudingcomplexities of other many details.

In considering this, it may be well first to recall that a one hundredpercent oxygen atmosphere can well be fatal to a diver in deepwater, eg.100 feet even if I breathed for only a very short time, and that loweroxygen partial pressures are equallyor more dangerous particularly asthe breathing time is longer or more rapid due to activity. Therefore,any system wherein oxygen partial pressure can rise beyond safe limitsmust provide against the occurrence of an over-oxygenated atmosphere byall possible means if it is to fulfill the safety demands of a systemuseful beyond the critical depth for pure or high partial pressureoxygen breathing. The system of the prior Pat. No. 3,252,458 includeselectronic circuitry designed to maintain oxygen at a level selected bythe diver. In this respect, the circuitry is well conceived and theoccurrence of too much oxygen would not ordinarily be expected to happenunder proper operating conditions of the equipment. However, assuggested above, it is again repeated that it is to be expected, in factforecasted, in providing oxygen such that it becomes immediatelyapparent to the diver, that all of the control equipment is for somereason totally inoperative and that emergency procedures are necessaryto be employed. This is especially advantageously applicable to theprotection of human life, it is applicable in the maintenance of asuitable atmosphere or other critical condition regardless of the objectof protection or the condition desired to be maintained.

The invention in structure and modes of operation is exemplified hereinby illustrating and describing underwater breathing apparatus of theself-contained closed circuit type, recently, and now more prominently,coming into use by divers. The invention is especially useful forrelatively deep diving but it is equally adapted for shallow water.

Generally described, and as revealed by the prior art, the closedcircuit type of diving equipment involves inhalation and exhalationwithin the confines of the equipment. Thus, normally none of the gasesare discharged from the equipment except on ascent, when it is necessaryto release internal pressure. Known units, such as shown in US. Pat. No.3,252,458, in-

clude a carbon dioxide absorber thru which the gas atmosphere is passedon inhalation or exhalation, the level being constantly monitored andreplenished up to a predetermined level. As will be understood,therefore, this type of system is highly desirable because no oxygen iswasted on exhalation, and the diluent gas, usually (costly) helium indeep water, is completely conserved. Consequently, longer periodunderwater ventures are readily feasible and at very great saving incost of helium.

The aforementioned US. Pat. No. 3,252,458 is believed to constitute themost closely allied description of apparatus relative to the presentinvention. This prior teaching employs an oxygen sensing device of theclass disclosed in US. Pat. No. 3,000,805. The sensing device as used inactual oxygen concentration determination is, or may be, technicallydescribed as a polarographic cell. The cell is positioned in the gasstream for contact therewith following the carbon dioxide eliminationstage. The cell operates to deliver a minute electric signal varyingwith the concentration of oxygen in the stream, oxygen actuallypenetrating into the cell and effecting a flow of current according toits' partial pressure. The electric signal thus developed is utilized byassociated electric circuitry to operate oxygen input means whereby thediver is supplied with additional oxygen from the oxygen tank as needed.

vances will be seriously hampered by refusal of people to work in theart. In other words, practicalities considered, the ultimate in possiblesafety is needed. To this end, quality in component parts is essentialand it is of prime importance that the entire system function properlyas an assembly. Even though such be provided, failures in any equipmentmust be recognized as inevitable.

Serious failures are minimized to an extremely high degree by thepresent invention and such as may possibly occur in using this inventionare reduced to a level of substantially zero criticality. This is incontrast to the prior levels of achievement of other workers whichleaves much to be desired. As aforesaid the teaching of the prior artare notable and it is not intended unduly to speak disparagingly ofthem. However, the prior art stopped seriously short of the desirableunderwater safety standards in a number of respects, and it must bepointed out that the known teachings'and equipment expose the diver toextremely dangerous conditions in the event of a particular type ofelectronic and/or associated equipment failure. Unfortunately suchequipment failure is inherently possible and quite likely to occurespecially in the course of use of equipment over a long period of time.This particular fault will be described more fully in relation to thepresent invention; however, a few brief comments at this point willserve to bring the matter to sharp focus absent surrounding shroudingcomplexities of other many details.

In considering this, it may be well first to recall that a one hundredpercent oxygen atmosphere can well be fatal to a diver in deep water,e.g. 100 feet even if breathed for only a very short time, and thatlower oxygen partial pressures are equally or more dangerousparticularly as the breathing time is longer or more rapid due toactivity. Therefore, any system wherein oxygen partial pressure can risebeyond safe limits must provide against the occurrence of anover-oxygenated atmosphere by all possible means if it is to fulfill thesafety demands of a system useful beyond the critical depth for pure orhigh partial pressure oxygen breathing. The system of the prior Pat. No.3,252,458 includes electronic circuitry designed to maintain oxygen at alevel selected by the diver. In this respect, the

The aforesaid US. Pat. No. 3,252,458 constitutes a consideration farmore feasible. However, the hazards are so great as to command thegreatest possible degree of certainty of continuously perfectsuitability to the needs of the diver as they suddenly developunderwater; otherwise underwater technological adcircuitry is wellconceived and the occurrence of too much oxygen would not ordinarily beexpected to happen under proper operating conditions 'of the equipment.However, as suggested above, it is again repeated that it is to beexpected, in fact forecasted, in providing any equipment for such highlyhazardous environment, that failures not at all necessarily the fault ofan inventor will occur as an inevitable matter, the life of the diverbeing in the balance.

Electronic systems in general such as are disclosed by the prior art aresubject to at least two types of criti-.

cal failures. The first is obvious, namely an occurrence involving aninstantaneous cessation in thecurrent flow such that it becomesimmediately apparent to the diver, that all of the control equipment isfor some reason totally inoperative and that emergency procedures arenecessary to be employed. This type of situation is indeed very seriousand the diver can be in grave danger, especially at considerable depth;but this is a-situation which heretofore in general has been taken intoaccount and emergency procedures have been established whereby the divermost probably will be able to reach the surface. However, some of theprior proposals are themselves a serious danger. For example, oneapproach is to supply a continuous flow of oxygen at about the minimumneeded for breathing, the

minimum oxygen flow being independent of the electronic metering systemwhich supplies a selected additional optimum quantity. Thus, the divercan theoretically make his way to the surface without harm. However,providing the same minimum flow at all depths, requires a complex massflow regulator which is prone to malfunction and does not take intoaccount the fact that physiological requirements for oxygen may vary bya factor to ten depending upon diver activity. The minimum flow approachis thus inherently prone to dangerous over or under oxygenationdepending upon activity and minimal flow selected.

As aforesaid, this type of electronic failure involves a complete andinstantaneous failure in the system whereby the metering means does notdeliver oxygen in the predetermined desirable quantity. However, thereis another type of failure, evidently not perceived by the prior workersin the art, such being of a less apparent and more subtle nature notinvolving instantaneous inaction of the metering system or circuitry.The fault in this instance involves a slow degradation from properfunction as for example in the sensing unit or amplification section. inthe course of which the system continues to operate, but imperfectly.This may be described as a malfunction and, though not common, doesoccur. If, for example, the malfunction occurs in the sensing cell, oramplification circuitry, it will effect delivery of excess orinsufficient oxygen (depending upon whether the signal output decreasesor increases), the remaining equipment functioning normally, theatmosphere will shortly become over-or under-oxygenated. Moreover, allindications from the equipment will read normal since the sytem will addor fail to add oxygen in whatever quantity is required to hold thesignal output at the predetermined level, i.e., meters will show theoxygen content to be at, or reasonably near the proper level, alarmswill not sound, and the diver will notbe warned. The result can easilymean death to the diver from oxygen poisoning or anoxia unless aco-diver is alert and observes abnormal behavior on the part of theendangered man. If such good fortune prevails, emergency procedure whichmay for example involve interchange of the breathing mouthpiece betweendivers can be employed while proceeding to the surface in apredetermined orderly manner, i.e., in view of decompressionrequirements.

Within the limits of reasonably feasible precautionary measures, and itbeing indisputible that absolute safety can only be approached and neverquite reached, the present invention enhances the inherent safeness ofthe breathing system by such magnitude that the hazard of over orunder-oxygenation as a matter of probability due to equipment failurebecomes substantially non-existent.

Before proceeding to other attributes of the invention, which are ofsubstantially of the same order. of

enhancement over known equipment, it is thought to be desirable todiscuss the necessity of diver interrelation an/or interfunction withthe breathing equipment. Such discussion follows in the succeedingparagraphs.

Insofar as is known, no attempts have as a practical matter beensuccessful in interrelating diver equipment with a measurable bodyfunction in order that the diver may be warned directly of possibleimpending unconsciousness following equipment failure or malfunction.Therefore, in the use of presently available equipment, the diver mustvisually observe indicators and heed audible signals in order to protecthimself in the event of equipment failure. Prior devices, particularly,for example, that according to U.S. Pat. No. 3,252,458 requiressubstantially continuous noting of the operating state of the system.Likewise, the present invention involves diver meter observance andattention to warning. However, the present invention goes far beyondprior provisions for warnings and, more importantly, the presentinvention provides the diver with actual analytical knowledge of thestate of the system to an extent and of a kind far transcending theprior art. Although the diver is required to note and act upon theavailable information provided by the invention herein, his failure todo so for an extended period of time is not likely, by the very greatestprobability, to leave him in serious circumstances. Stated in anotherway, though it is quite desirable for a diver to observe the state ofthe equipment every minute or so, the present invention affords such ahigh degree of protection against internal equipment malfunction thatthe diver is provided with a very great margin for human failure.

The abstract of the invention will have provided an introductory amountof understanding of the present invention such that upon reflection inthe course of considering the foregoing discussion, the basis forindicating the remarkable advances may be well appreciated.

' oxygen concentration in the system. If, for example, the

alarm circuitry were to be involved in a failure'in the system, theoxygen concentration might be dangerously out of line even though theindicating meter indicated a 0 normal and safe breathing atmosphere. Thediver is entirely at the mercy of the equipment and any suspectindication must be taken as an emergency.

In overcoming the disadvantages referred to above-in equipment of theclosed circuit, self-contained type, and in related types ofapplications where oxygen concentration is critical or to be controlled,the present invention preferably employs three oxygen sensing ormonitoring units, such being of the general type disclosed in U.S. Pat.No. 3,000,805. As aforesaid, these monitoring units, or cells provide aminute voltage which is proportional to oxygen concentration, thevoltage varying accordingly with such concentration. The output of thecells being extremely small, three separate amplification sections areprovided, each amplifying the signal from its respective signal source,that is, each cell respectively. Each amplified signal is measuredthrough an isolating resistor by a microammeter which is scaled fromzero to 100, the full scales being linearly representative of oxygenpartial pressure of from about zero to about one atmosphere, individualcell outputs of from zero to about volts, (more realistically about 4.7volts in a practical operating circuit,) corresponding to the partialpressure scale. Accordingly, an amplified cell output of approximately2.4 volts (practical embodiment, about 2.35) corresponds toapproximately 0.5 atmospheres oxygen partial pressure.

The three signals are further processed by electronic circuitry wherebyan average voltage is obtained which is thereafter processed to operatea solenoid oxygen input valve. The solenoid valve is set to deliveroxygen at times when the average amplified voltage falls below about 2.4volts. Thus, the system normally operates to fulfill one of its intendedobjects, that is the provision of an oxygen concentration ofapproximately 0.5 atmosphere in the system. Under normal operatingconditions it is not usual that the oxygen concentration would risesignificantly above 0.5 atmosphere, since the supplied oxygen isconstantly depleted by the diver in breathing. However, in normaloperations of the equipment the solenoid valve remains closed when theaverage voltage rises to or above about 2.4 volts.

The system includes audible alarm circuitry deriving a signal from eachof theamplified cell voltages. The alarm is electronically set to givewarning if any one cell voltage falls below about 1.9 volts or risesabove about 3.3 volts. The said range of 1.9 volts to 3.3 volts will beseen to correspond approximately to about 0.4 and about 0.7 atmospheresoxygen partial pressure, thus providing a range for tolerable oxygenconcentration and safe breathing by the diver.

Although the present invention contemplates still further and highlyimportant features tending to insure the safety of the diver, it ispointed out that the association of equipment described immediatelyabove affords the diver several advantages in that the three independentsignal provide him with intelligence which when coupled with his basicknowledge of the characteristics of the system enable him to reachconclusions concerning the probable state of the equipment that is notpermitted by one signal, or even two signals. As will be understood, andas indicated above, a single signal affords little reliable evidence.Two signals at variance with each other merely leaves the diver in aquandry as to which signal is the correct one. Three signals, however,enable him to compare'two against one and consider the intelligence as amatter of probability. The probability of two sensors being in error is,of course, the square of the probability of one being in error, and thatprobability decreases with decreasing time; hence the probability of twosensors malfunctioning or failing at the same time is substantiallyzero. Since the system will also function within safe limits on only twosensors, the same high probability of safe operation applies to theoxygen control signal. Additionally, the three signals provide a moreaccurate measure of the oxygen concentration in the respect that theaverage of the three .signal tends to compensate for internal componentvariation from indicated values. As is well known, electronic componentsare true to their rated values on the basis of plus or minus about 10percent plus or minus 5 percent in highly select components. Internalinaccuracy of this type is compensated for in proportion to the numberof separate signals processed through the electronic averaging means. Inthis respect it should be apparent that even two monitoring andamplification stages provide improvement in accuracy of the finalapplied signal. It may be mentioned in this connection, that thisinvention provides means in the electronic system serving as anadjustment upon each amplified monitoring output whereby, in the main,such internal inaccuracies are compensated for..monitoring Further,however, the preferred embodiment of this invention includes additionalelectronic circuitry whereby any one or all of the amplified voltages isclipped or held at about 1.9 and 3.3 volts should it fall or rise tothose limits. This clipping prevents an erroneous signal from pullingthe average voltage, and hence oxygen concentration outside of safelimits. in this way the system continues to function reliably so long asthe remaining two oxygen monitor signal are a reliable or correctmeasure of the actual oxygen concentration in the system. Thus, in thepresent system where three monitors are employed, one of them may beeffectively eliminated and the remaining cells or monitor signals asamplified and averaged with the clipped output of the erroneous sensorwill continue to deliver oxygen within the established range, and,moreover, such remaining monitor signals are effective continuously toprovide the oxygen concentration at near the optimum of about 0.5atmosphere. 7

The audible alarm sounds at the time of voltage clipping; therefore, thediver is made aware of the questionable functioning of the equipment,although he may have noted a disturbing condition theretofore byobservation of the partial pressure indicators.

The invention further contemplates the use of a 7 separate oxygenpartial pressure indicator, the same being self-contained and powered,and being provided with a microammeter reading in terms of oxygenpartial pressure as the other meters of the main system. Such additionalpartial pressure indicator is contemplated as being constructed entirelyelectrically similarly to the monitor cells, the amplification circuitryand the indicator circuitry of the main equipment. Being entirelyself-contained, however, it is contemplated that such unit may beemployed either in combination with the main equipment, being adapted toprobe the internal oxygen atmosphere thereof and respond to providecorroboration of any or all partial pressure indicators in the mainsystem, or, it being useable in the event of failure of two sensors oreven total failure of the main equipment whereby manual oxygen feed maybe accomplished with knowledge of the concentration as afforded by theadditional unit.

As was pointed out in the abstract presented at the forepart of thisspecification, the present invention proceeds from the point of viewthat in the continual usage of the equipment the probability ofsimultaneous failure of two signals in any possible respect isconsidered to be substantially zero. This conclusion is not only amatter of mathematics but it is based upon the facts that such equipmentis contemplated as being constructed of very high quality components andassembly quality control being of the highest, both facts being inconsideration of the extreme hazards that are involved in underwaterwork and the desire to enhance the base factors involved in thetime-probability calcufail due to its own characteristic and that uponsuch happening if the equipment is thereafter to be realisticallyuseable by the diver, the system must provide him with means fordetermining with substantially equal certainty which signal of anassembly of signals is in error. This is accomplished by providing atleast three informative signals. The above-mentioned probabilityconsiderations are effectively meaningful in a diver system involvingthree signals, the diver observing the indications of two like signalshaving the high probability of correctness, and comfortably relyingthereon in conducting himself in the emergency situation.

It should be appreciated that the advantages of the time-probabilityfactor as embodied in the present invention are extremely great;however, the invention proceeds beyond such point and, in the preferredembodiment, provides automatically for the continued operation of theequipment based upon the two remaining signals without the need for anyattention whatsoever on the part of the diver. Considering theimportance of surely providing for a minimum oxygen concentration andagainst amounts above a predeterminedmaximum oxygen concentration at alltimes, the feature of automatic operation to continue concentrationwithin the limitation is regarded as quite important in that there is notime delay involved in adjusting the equipment when a signal is atvariance with the true concentration present in the system. The presentsystem relieves the diver completely of any concern regarding thereliability of the system insofar as oxygen content is concerned, and heis free to start his ascent to the surface at once without the necessityfor making adjustment; and notably important, in an unalarmed mentalstate. Further, highly important is the fact that even though the alarmshould fail to sound at the proper point, the probability of diversafety is not significantly lessened. This is because of the fact thatthe probability of a second failure before surfacing is extremely low;moreover (in following standard diving procedure,) the diver will havevisually noted a failure and will have aborted the'dive long before timeunder water admits of a second failure.

It is recognized that modifications of the basic approach to the systempreferred herein are possible. For

example, a two signal system supplemented by an ex-' terior probesensor-indicator affords substantial possibilities for increasedinformation andsafety. Yet, in such case, precious manipulative time isinvolved. Thus, it is believed that deviations from a system includingat least three signals, coupled with automatic continued safe operationfollowing the loss of one, is very difficult, if not impossible, tojustify in view of the safety hazard that is involved. Where inanimatesubjects are regulated in accordance with the teachings of thisinvention, it is recognized that some relaxing of strict adherance tothe approach of the ultimate in reliability and operation may bejustified.

FIG. 3 is a sectional view of an oxygen detection or sensing meansemployed in each of three monitoring stages of FIG. 4; and

FIG. 4 is a circuit diagram of the electrical monitorcontrol system.

Referring to FIG. 1 of the drawings, the entire apparatus is shown inthe form of a layout showing the positioning and relationship of thevarious parts. FIG. 2 may simultaneously be considered. In the drawingsnumeral l0 refers to a tank for pressurized oxygen and numeral 12 refersto a tank forpressurized helium, or other inert gas. Since the apparatusis of the closed circuit type, the system contains a carbon dioxideabsorbing cannister denoted by numeral 14 containing an absorbentmaterial 16. Numeral l8 denotes an expansible breathing bag whichreceives air discharged from the lungs upon exhalation. Numeral 20denotes a breathing mouthpiece through which air is inhaled and exhaled.The breathing tube circuitry comprises a conduit 22 interconnecting themouthpiece into the circuit. Numeral 24 denotes a conduit connectinginto conduit 22 through which the oxygen-helium mixture is drawn oninhalation, numeral 26 denotes a conduit leading to the breathing bag 18and numeral 28 denotes a conduit leading off of conduit 26 through whichinhaled gas passes into the carbon dioxide absorbing zone before beingdrawn through conduit 24 to the mouthpiece. Numerals 30 and 32 denotecheck valves for controlling the direction of flow of the gases uponinhala tion and exhalation. As will be observed check valve 30 isdesigned to open upon inhalation and, at the same time, check valve 32closes, so that gases are drawn from the breathing bag through theabsorbent cannister to the mouthpiece. Upon exhalation, valve 32 opensto permit the passage of exhaled gas into the breathing bag, valve 30closing simultaneously. All of the foregoing parts are well known instructure and function and do not require further detailed description.

Numeral 34 denotes an isolated portion of cannister 14 which portion maybe described as a chamber of the apparatus for containing the means forinjecting oxygen into the system and the means for monitoring or sensingthe oxygen content of the circulating gases. Chamber 34 is in directfluid communication with the carbon dioxide absorber, as may be seenupon reference to FIG. 2 via a perforated plate or screen there shown atnumeral 35. As will be seen, conduit 24 connects into chamber 34. Also,as will be seen, tube 28 connects into conduit 36, (see FIG. 2,) thelatter directing the .gases to the extreme end of the carbon dioxideabsorber where it enters chamber 38, from which it passes reversely intoand through the absorbent via perforated divider plate 39, more clearlyseen in FIG. 2, upon inhalation. Chamber 38 is merely a sec tion of theoverall cannister 14, the plates being therein to form a zone forretaining the carbon dioxide absorbent. Inhalation then continues todraw the gas mixture then denuded of carbon dioxide, through theabsorbent into chamber 34 where its oxygen content is monitored, andfrom chamber 34 the gas mixture passes through conduit 24 to the divervia the connecting mouthpiece. Thus, the circuitry includes the passageof the gas from the breathing bag on inhalation through the circuitryleading to the carbon dioxide absorber and re-breathing of the exhaledgas, it being drawn through the absorber via conduit 24, the gas in itspassage being treated for carbon dioxide removal, and

having its oxygen supply replenished as necessary.

Oxygen replenishing takes place in chamber 34. As will be observed, theoxygen supply 10 is connected to a solenoid operated valve 40 mountedwithin chamber 34, oxygen line 42 providing for delivery of oxygen fromthe tank via the regulator 44C. Line 42 connects to the oxygen supplytank via manually operable valve assembly 44 which valve is open whenthe system is in use and closed when it is not.

Replenishment of oxygen occurs as the quantity of oxygen in the systemlowers following its usage by the lungs and subsequent conversion tocarbon dioxide.

The gas mixture in the system is continuously monitored for oxygencontent in chamber 34 as it flows therethrough. The monitoring isaccomplished by a plurality of polarographic electrolytic cells, numeral46 which vary their voltage output according to the oxygen content ofthe gas mixture. The plural assembly of the cells will be described ingreater detail at a later point herein. In general, however, it may bementioned at this point that each individual cell contains a liquidelectrolyte which absorbs oxygen from the 'gas stream across a membrane.Thus, the higher the partial pressure of oxygen in the gas mixture thegreater will be the amount of oxygen absorbed by the cells. Converselylesser oxygen partial pressure results in a smaller oxygen absorption.As aforesaid, the output of each cell varies with absorbed oxygen,output being greater with higher oxygen content and less with smalleroxygen content.

The output of each cell is delivered to an electronic processing systemdenoted generally by numeral 48, this system being housed, together withbatteries, in separable chamber 49. The resulting signal from theelectronic processing is employed as a control for the solenoid valve40. The monitor and control system is designed and electricallyproportioned to maintain the oxygen supply as nearly constant aspossible, as related to a predetermined desirable oxygen partialpressure in the gas mixture. A more complete discussion of this aspectof the invention in relation to desirable physiological conditions, theelectronic circuitry and the related cells, will appear hereinafter.Before proceeding with such further discussion it is desirable tocomplete a general description of the overall assembly.

The helium supply tank 12 is connected to chamber 38 via line 50. Line50 connects into a valve assembly 52. Valve 52b is manually operable andserves to add helium to the gas mixture by the divers manipulation inresponse to decreasing volume (deflation) of the breathing bag. As willbe understood, as long as the exterior pressure resulting from the depthof the water remains constant, the gas volume in the system normallywill remain constant. However, as the diver descends, pressure increasesand the pressure increase is reflected by a deflation of the breathingbag, The volume required for full inhalation is resupplied when valve52b is opened, whereby helium is admitted in sufficient quantity tobring the volume of gas in the breathing circuitry back up to the properlevel. Similarly, upon ascent the internal pressure must be relieved.Such release of pressure is readily accomplished by breathing outwardlyaround the mouthpiece or thru the nose, or a relief valve may beemployed in the system. It will be understood that the helium volume maybe automatically supplied in response to internal demands. For example,this may be accomplished by a demand regulator of any well-known type.

Numeral 60 denotes a oxygen content indicator assembly which serves toinform the diver of the oxygen content of the stream as reflected by thecells. The metering assembly will be more fully described at a laterpoint but it may now be stated that it includes 3 meters,

i.e., a separate meter for each cell, thereby separately reflecting thecondition of each one of them. The indication is provided constantly andthis assembly permits the diver to know immediately of deviations ofeach cell from its expected normal output as well as any change inoxygen partial pressure as indicated by all of the meters. The indicatorassembly connects into the circuitry via leads 62.

Since the oxygen supply at all times is absolutely critical, oxygen tank10 is provided with a by-pass line 64 leading into chamber 38, throughwhich line oxygen supply may be manually delivered by a valve 44b. Aswill be understood, such valve is normally closed and oxygen would notpass through this line except under emergency conditions, or when usingpure oxygen for decompression at shallow depths.

Referring again to FIG. 2, it will be seen that separable chamber 49,the cannister section 14, and enclosing endplates 65 and 66 are held inassembled relationship by rod 68 which threads into one endplate througha waterproof gland in the other endplate thus tying the entire assemblytogether. The spring 70 seen in chamber 38 serves to hold the orificeplate 72 in position thereby to maintain the absorbent material withinthe desired zone.

The relatively thick member denoted by numeral 74 seen between chambers34 and 49 serves a number of thru the wall 76 thereby enabling theexterior actuation of switch unit 80 within chamber 49.

It may be pointed out that member 74, positioned and serving asdescribed affords significant advantages when it is necessary to serviceany component of the unit. This becomes apparent in noting that all ofthe sensing and control equipment is removable and, so removed, is heldas a single assembly upon the member 74. The only attachment of themember to the device as a whole is then by way of oxygen line 42, whichis easily detached. Further, a malfunctioning assembly may quickly andeasily be replaced by setting a new assembly in position.

Further, the manner of assembly and provision of chambers affords theadvantage that additional chambers may be added, e.g. similar to and inthe manner in which chamber 49 is provided. For example, it may bedesirable to attach a special communication module and as will beapparent such may be easily done. The cannister-chamber units andendplates are fitted tightly and are rendered watertight as by sealingO-rings, gaskets, such as at numeral 92. Of course, all fittingsattaching to the assembly are similarly made watertight.

The materials employed in the construction of the cannister-chamberassembly may be as desired; how ever clear plastic such as Lucite isquite satisfactory and offers the advantage of visual inspection formoisture and absorbent condition while diving.

The material employed for carbon-dioxide removal is well known, it beingsold under trade name Barylyme, and being composed mainly of bariumhydroxide which absorbs by reacting to formbarium carbonate. Anindicating color change is incorporated to indicate when its absorbingcapacity is exhausted.

Referring to FIG. 1, the tanks and cannister-chamber section areassociated together by releasable metal band 82. The tanks and cannisterchamber section are separated by nesting blocks 84 which conform to thecontour of the parts. Harness straps, as for example denoted by numeral86, anchored in blocks 84 serve to hold the apparatus securely to thediver. The breathing bag 18 attaches to the harness via twist studswhich are mounted on the harness and lock into the breathing bag at theshoulders and lower corners (90). The breathing bag may be of materialsas desired; however clear flexible plastic such as vinyl is satisfactoryand offers the advantage of visual inspection for water inside the bag.A small plug 18A provides a drain for removal of water resulting fromcondensation or leakage around the mouthpiece.

The mouthpiece 20 is provided with a valve 94 serving to open and closethe breathing circuit as and when desired.

Since the gas cylinders are under high pressure, needle valves areemployed as a means to permit a controlled flow without experiencingheavy blasts into the equipment. Thus, valves 44b and 52b include such,and the orifice 96 for gas dischargefrom the solenoid valve 40 is of atype permitting flow regulation-Ideally the discharge from the solenoidvalve is adjusted so that it overrides the control point by to percentof an attrode 114 (for example, numerals 209 and 210 of FIG. 4) whichmay suitably be respectively of platinum and silver, the latter having athin coating of silver oxide thereon. The electrodes, being mountedconcentrically, are separated by any suitable insulating material, e.g.a plastic mass denoted by numeral 116. Leads 118 and 120 serve toconnect the device into the electronic circuitry as seen in FIG. 4. Thethermistor 207 seen in FIG. 4, (not shown in FIG. 3), may be mounted onthe sensor retaining member 122 or may be cast in the base 116 of theelectrode assembly itself so as to be in the same temperatureenvironment as the sensing means itself. Retaining member 122 is simplya sheet or bar of any suitable material, e.g., acrylic plastic, bearinga tapered hole 126 into which the electrode assembly is inserted in themanner of a stopper. It acts only as a holder for the electrodeassembly. Numeral 46 of FIG. 1 indicates such a holder with three holesfor the three separate electrode assemblies. Numeral 130 denotes aliquid electrolyte, for example, potassium hydroxide, the same beingcontained between the electrodes in a shallow circular channel formed bythe electrodes extending beyond the insulating mass 116.

Numeral 134 denotes a oxygen-permeable membrane which may be ofpolyethylene or any suitable mosphere, thus it is activated for onlyabout 3 seconds A similar pressure indicator may be provided for thehelium tank.

Numeral 100 denotes the alarm which suitably is 'material. As will beseen, the membrane fits tightly downwardly over the electrode and servesalso to retain the electrolyte. Numeral 136 denotes an outermembrane-retaining member having a pssageway 138 whereby the membrane isleft exposed to the oxygen atmosphere while being securely held in afixed position The membrane retaining member is of any suitablematerial, e.g., silicone rubber.

As aforesaid, the cell(s) herein employed are entirely similar indesign, operation and function to the cells described in prior Pat. No.3,000,805; and the disclosure of said patent is hereby made a part ofthis specification. It may be noted that the herein described cellprovides a shallow channel for holding potassium hydroxide, or similaracting material, rather than the cuitry is highly sensitive, it isimportant that the elecfixed to member 74, being connected into thecircuitry .as in FIG. 4.

A solenoid-valve assembly of highest efficiency is desirable in orderthat the lowest power drain will be made upon the batteries. Allowingthe inner plunger .maximum travel produces greatest useable power. Ac-

sensing means employed in the invention, the same being more fullydiscussed hereinafter in association -with the electrical circuitry. Inthis drawing numeral 110 (numeral 208 of monitor stage 200, FIG. 4)designates the type of operating cell of monitor stages 200, 201 and 202depicted in FIG. 4, including inner electrode 112 and outer surroundingcylindrical electrodes be as free of impurities as possible.

Referring now to FIG. 4, there is disclosed an illustrative embodimentof the electronic circuit of the present invention including threeoxygen monitoring stages 200, 201 and 202. As shown, the threemonitoring stages are energized from a suitable direct voltage source,illustrated as a single battery 203, via singlepole double-throw switch204. Switch 204 is ganged with other switches as will be made clearhereinafter. Each stage may be energized by separate batteries inpractice so that failure of a single battery will not disable all of themonitoring stages.

The first monitoring stage 200 includes a voltage divider consisting ofresistors 205 and 206 connected across battery 203 via switch 204 shownin a closed position. The voltage divider may be constructed as apotentiometer having a fixed or movable tap if desired. Connected inparallel with resistor 206 is temperature compensating thermistor 207and oxygen sensing electrolytic cell 208 connected in series. Cell 208includes a reference electrode 209 made of silver or other'suitablematerial, having a thin film of an oxide or other suitable material onthe surface thereof and a reaction electrode 210 made of platinum. Thecell includes an electrolyte, such as potassium chloride or potassiumhydroxide, between electrodes 209 and 210 as seen in FIG. 3. It is knownthat the current flow through electrolytic cells of the type used isproportional to the concentration of oxygen to which the cell issubjected. It is known that the current flow through electrolytic cellsof the nature of cell 208 is temperature dependent, and it is desirablethat temperature compensation be provided. Thermistor 207 has asubstantially equal but opposite temperature coefficient to that of cell208. In operation, the thermistor 208 is desirably so placed that itwill have the same temperature as that of the gaseous mixture beingsensed. The current provided through cell' 208 causes a voltage dropacross thermistor 207. The output from monitoring stage 200 is takenacross thermistor 207 and appears as a positive voltage on lead 211connected to one side of thermistor 207. The other side of thermistor207 is connected to ground.

Oxygen monitoring stages 201 and 202 are constructed in the same fashionas oxygen monitoring stage 200, and are likewise energized from battery203 via switch 204. Monitoring stage 201 includes a voltage dividerconsisting of resistors 212 and 213 connected across battery 203 viaswitch 204. A series connected thermistor 214 and oxygen sensing cell215 are connected in parallel with resistor 213. Electrode arrangement215 includes a silver reference electrode 216 and a platinum reactionelectrode 217. The output from monitoring stage 201 is taken acrossthermistor 214 and appears as a positive voltage on lead 218 connectedto one side of thermistor 214, the other side of thermistor 214 beingconnected to ground. Oxygen monitoring stage 202 includes a voltagedivider consisting of resistor 219 and resistor 220 connected acrossbattery 203 via switch 204. A series connected thermistor 221 and oxygensensing cell 222 are connected in parallelwith resistor 220. Oxygensensing cell 222 includes silver reference electrode 223 and platinumreaction electrode 224. The output from monitoring stage 202 is takenacross thermistor 221 and appears as a positive voltage on lead 324connected to one side of thermistor 221, the other side of thermistor221 being connected to ground.

The three distinct voltage outputs from the three oxygen monitoringstages are fed via leads 211, 218 and 324 to signal-processingamplifiers 225, 226 and 227, respectively. The details ofsignal-processing amplifier 225 are shown. Signal processing amplifiers226 and 227, illustrated as boxes, are constructed identically to signalprocessing amplifier 225.

Signal-processing amplifier 225 includes a directly coupled linearoperational amplifier 228 and a signalclipping stage 229. The signaldeveloped across thermistor 207 is fed via line 211 to the positiveinput terminal 230 of directly coupled linear operational amplifier 228.The operational amplifier is provided with a ground terminal and anegative input terminal 236. The positive input terminal 230 ofamplifier 228 is connected to ground via capacitor 231. Numeral 232denotes the amplifier output terminal. A negative feedback path isprovided from the output terminal 232 to the negative input terminal 236of the operational amplifier 228. The negative feed-back path includesgain control variable resistor 233 and fixed resistor 234 connected inseries. A resistor 235 is connected between ground and the negativeterminal 236 of theoperational amplifier 228. The operational amplifier228 may be advantageously constructed as an integrated circuit, andshould have sufficient gain so that its output is from zero to about 5volts. A possible gain of about is desirable. A variable resistor 237 isconnected to appropriate terminals of the operational amplifier 228 orforms a part thereof for zero setting the operational amplifier 228. Theoutput from terminal 232 of the operational amplifier 228 appears atpoint A which is connected via isolating resistor 238 to ground throughmicro-ammeter 239. Isolating resistor 238 is preferably large enough sothat even were microammeter 239 or the leads thereto-shorted, thevoltage at point A would not be significantly changed. The output fromterminal 232 is also connected to point E via resistor 240. Point E isconnected via resistor 241 to the negative input terminal 242 of adirectly coupled averaging amplifier 243. The positive input terminal244 of averaging amplifier 243 is connected via resistor 245 to apositive 2.4 volt terminal 294 of regulated power supply 295. Theregulated power supply 295, which will be described in detail below,further includes a negative 6.75 volt terminal 296, a positive 6.75 voltterminal 297, and a ground terminal 298.

Point E, the junction between resistors 240 and 241 is also coupled tosignal clipping stage 229 which includes two normally nonconductivetransistors 247 and 252. Point E is connected directly to the emitterelectrode 246 of normally nonconductive npn transistor 247. Thecollector electrode 248 of transistor 247 is connected to the positive6.75 volt terminal 297 of regulated power supply 295 via resistor 249.The junction between collector 248 and resistor 249 is designated pointB. Point E is also connected via germanium diode 250 to the emitterelectrode 251 of normally nonconductive pnp transistor 252. Thecollector electrode 253 of transistor 252 is connected to the negative6.75 volt terminal 296 of the regulated power supply 295 via resistor254. The junction between col lector 253 and resistor 254 is designatedpoint C. The base electrodes 255 and 256 of transistors 252 and 247,respectively, are connected to the positive 24 volt terminal 294 of theregulated power supply 295. The transistors 247 and 252 havebase-emitter characteristics such that the base-emitter path becomesconductive whenever about one-half a volt appears between the base andemitter electrodes. The characteristic of germanium diode 250 is suchthat it becomes conductive in a forward direction whenever about 0.4volt appears between its plate and cathode.

Signal processing amplifiers 226 and 227 are constructed identically tosignal processing amplifier 225 described above, and will not beseparately described in detail. The points corresponding to point A,point B, point C and point E are shown for signal processing amplifier226 as points A, B, C, and E; respectively, and for the signalprocessing amplifier 227 as points A, B, C" and E", respectively. As canbe seen, points B, B and B" are connected together, and points C, C andC are connected together. The base terof signal processing amplifier 227is connected to ground via series connected large isolating resistor 257and microammeter 258. Isolating resistor 257 also is a large resistor,and serves the same function as resistor 238 mentioned above. Point E,at which the output from signal processing amplifier 226 appears, isconnected via resistor 259 to the negative terminal 242 of directlycoupled averaging amplifier 243. Point E", at which the output fromsignal processing amplifier 227 appears, is connected via resistor 260to the negative input terminal 242 of directly coupled averagingamplifier 243. Resistors 241, 259 and 260 are the same size. The outputof direct current averaging amplifier 243, an operational amplifier,appears at point D which is connected via resistor 261 to the baseterminal 262 of normally nonconductive npn transistor 263. The emitterterminal 264 of transistor 263 is connected to ground. The collectorterminal 265 of transistor 263 is connected to the positive 6.75 voltterminal 297 of the regulated power supply 295 via resistor 266. Thecollector electrode 265 is also connected via resistor 267 to the baseelectrode 268 of normally nonconductive pnp transistor 269. The emitterelectrode 270 of transistor 269 is connected to the positive terminal ofbattery 271. The collector terminal 272 of transistor 269 is connectedto the negative terminal of battery 271 via series connected single-poledouble-throw switch 273 and the oxygen control solenoid 40.

As mentioned above, the collectors of the signal clipping transistors247 and 252 are coupled respectively to the positive 6.75 volt terminal297 and the negative 6.75 volt terminal 296 of the regulated powersupply 295 via resistors 249 and 254 as are the collectors ofcorresponding transistors, which are not shown,

but form a part of signal processing amplifiers 226 and 227. Points B, Band B" are also connected to a first input line 275 of alarm circuit276. Line 275 is connected via resistor 277 to the base electrode 278 ofnormally nonconductive pnp transistor 279. The collector electrode 280of transistor 279 is connected to one terminal of audible alarm 281. Theother terminal of audible alarm 281 is connected via single-poledouble-throw switch 282 to the negative terminal 296 of power supply295. The collector 280 is also connected to the collector electrode 286of normally nonconductive pnp transistor 285 which has its emitterelectrode 287 connected to the positive 6.75 volt terminal 297 of theregulated power supply 295. The positive 6.75-volt terminal 297 ofregulated power supply 295 is connected via series connected resistors288 and 289 to the base electrode 390 of transistor 285. The junctionbetween resistors 288 and 289 is connected to the collector electrode290 of normally nonconductive npn transistor 291. The emitter electrode292 of transistor 291 is connected to the negative 6.75 volt terminal296 of the regulated power supply 295. The base electrode 293 oftransistor 291 is connected to point C of signal processing amplifier225 and points C' and C of signal processing amplifiers 226 and 227.

The regulated power supply 295 includes a battery pack consisting offour 9 volt batteries 299, 300, 301 and 302. Batteries 299 and 300 areconnected in series through single-pole double-throw switch 303 topositive 6.75 volt terminal 297 via resistor 304. Resistor 305 and a 2.4volt Zener diode 306 are connected between terminal 297 and groundterminal 298. The positive 2.4 volt terminal is provided at the junctionbetween Zener diode 306 and resistor 305. Connected in series betweenthe positive 6.75 volt terminal 297 and the negative 6.75 volt terminal296 is series connected resistor 309 and the collector emitter path ofnpn transistor 310. The base electrode of transistor 310 is connected tothe positive 6.75 volt terminal 297 via series connected 6.25 volt Zenerdiode 308 and 6.75 volt Zener diode 307. Switches 204, 282, 273 and 303are preferably ganged together so as to simplify operation of thecircuit. While all of the switches are shown as single-pole double-throwswitches, only switch 303 serves to connect different elements into thecircuit. In the position shown in the drawing, switch 303 connectsseries connected batteries 299 and 300 to the regulat-' ing part ofpower supply 295. In such a position seriesconnected batteries 301 and302 are held in reserve. In the event battery 299 or battery 300 failsor becomes too low in voltage, switch 303 is used to switch to freshreserve batteries 301 and 302.

In a practical embodiment of the illustrated circuit of the presentinvention, the values and identification of components used are asfollows:

resistor 205 500 0 variable resistor 233 0-30K O resistor 206 1000 .0.

variable resistor 212 500 Q resistor 237 O-SOK fl resistor 213 1000 Qoperational T-52 amplifier 290 Philbrick resistor 219 500 Q averagingT-52 resistor 220 I000 Q amplifier 243 Philbrick resistor 234 3.9K!)capacitor 231 H) p. resistor 238 47K (1 transistor 247 2N 3903 resistor240 68KB transistor 252 2N 3905 resistor 241 27K 0 transistor 263 2N3903 resistor 245 10K 9 transistor 269 2N 1309 resistor 249 27K 0transistor 279 2N 3638 resistor 254 27K!) transistor 286 2N 3638resistor 255 47K [2 transistor 291 2N 3903 resistor 257 47KB transistor310 2N 3903 resistor 259 271) Zener diode 306 2.4 volts resistor 26027K!) Zener diode 307 6.75 volts resistor 261 27 K0 Zener diode 308 6.25volts resistor 266 K!) resistor 267 2.7K!) resistor 277 27K 0 resistor288 lOOKfl resistor 289 27K .0

The matter of zero setting and calibrating the illustrative circuit ofthe present invention will now be described. Microammeters 239, 256 and258 have a scale from 0-100 1. amperes. Full scale deflection is chosento correspond to one atmosphere of oxygen. Zero deflection is chosen tocorrespond to complete absence of oxygen. First, ganged switches 204,282, 273 and 303 are placed in an on position as shown in the drawing.An oxygen free gas, such as propane, is supplied to oxygen sensing cell208 so that no oxygen appears between silver reference-electrode 209 and(platinum reaction electrode 210. Under these circumstances, cell 208provides no current representing the presence of oxygen and no outputrepresenting the presence of oxygen appears across thermistor 207.

Zero setting variable resistor 237 associated with operational amplifier228 is adjusted so that meter 239 reads zero, indicating the absence ofoxygen between electrodes 209 and 210. In a similar fashion, an oxygenacross thermistor 214and thermistor 221. Zero setting variableresistors, not shown, associated with directly coupled operationalamplifiers, not shown, within signal processing amplifiers 226 and 227are adjusted, in the same manner as variable resistor 237, so thatmicroammeters 256 and 258 also read zero indicating the absence'ofoxygen between electrodes 216 and 217 and between electrodes 223 and224. After microammeters 239, 256 and 258 have been zero set,oxygensensing cells 208, 215 and 222 are placed in a gaseousenvironment, such as air, containing approximately 20 percent oxygen atatmospheric pressure. Positive going outputs appear across each ofthermistors 207, 214 and 221 which are representative of the presence ofa gas containing 20 percent oxygen by volume at atmospheric pressurebetween electrodes 209 and 210, electrodes 216 and 217, and electrodes223 and 224, respectively.

' The positive going outputs are fed to the inputs of signal processingamplifiers 225, 226 and 227, respectively. The gain of directly coupledoperational amplifier 228 is adjusted by varying the value of variableresistor 233 in its negative feedback path. Increasing the value ofresistor 233 reduces the amount of negative feedback and increasesthegain of operational amplifier 228. Decreasing the value of resistor 233increases the amount of negative feedback and decreases the gain ofoperational amplifier 228. The gain is adjusted until microammeter 239deflects to 20 percent of full scale. When so set, the 20 percentdeflection represents an oxygen concentration corresponding to a partialpressure of 0.2 atmospheres supplied to oxygen sensing cell 208. Sinceoperational amplifier 228 is a linear amplifier, half scale deflectionwould represent a concentration of oxygen corresponding to0.5'atmosphere supplied to sensing cell 208.

In a similar manner, gain control resistors, not shown, associated withdirectly coupled operational amplifiers, not shown, within signalprocessing amplifiers 226' and 227 are adjusted so that microammeters256 and 258 deflect to 20 percent of full scale. When so set, 20 percentscale deflection on microammeters 256and 258 represent a concentrationof oxygen corresponding to a partial pressure of 0.2 atmospheressupplied to cells 215 and 222 respectively. Since the directly coupledoperational amplifiers in signal processing amplifiers 225 and 226 arelinear, half scale deflection on respective meters would represent aconcentration of oxygen corresponding to a partial pressure of 0.5atmosphere supplied to oxygen sensing cells 215 and 222, respectively.The circuit having been calibrated and zero set, is ready for operation.

Since ,the circuit has been calibrated in the manner set out above,positive voltages of approximately 4.7 volts, (1 atm.) at points A, Aand A and a full scale deflection of meters 239, .256 and 258 indicatesa concentration of oxygen corresponding to a partial pressure of oneatmosphere as determined from the outputs of oxygen sensing cells 208,215 and 222 respectively. Ideally, positive voltages of 2.35 volts atpoints A, A and A" indicates a concentration of oxygen corresponding toa partial pressure of 0.50 atmospheres as sensed by the correspondingoxygen sensing cells. As a practical matter, positive voltages of 214volts at points A, A and A" indicates a concentration of oxygencorresponding to a partial pressure of approximately 0.5 atmosphere assensed by corresponding sensing cells. Positive voltages at points A, A"and A'" of-approximately 1.9 volts would indicate a concentration ofoxygen corresponding to a partial pressure of approximately 0.4atmosphere, while positive voltages at points A, A and A" of about 3.3would indicate an oxygen concentration corresponding to a partialpressure of approximately 0.7 atmosphere is sensed by vcorrespondingsensing cells. 7

7 Having described the apparatus and associated circuitry, and themanner by which it is prepared for use, its 7 functioning in use by adiver is described hereinafter. As will be appreciated, such functioningis in particular regard to the occurrences taking place in theelectronic circuitry since the electrical system, beginning with theoxygen concentration monitors through to the solenoid operated valve,include the only variants, and otherwise the type of system is wellunderstood. Of course, it will be appreciated that the oxygen monitorstages 200, 201 and 202 correspond to the sensor assembly designated bynumeral 46 in FIGS. 1 and 2, and that the circuitry shown in FIG. 4'correspondsto that which is shown in block form in FIGS. 1 and 2 atnumeral 48. All switches included in the circuitry must be in the onposition, namely, switches 204, 273, 282 and 303, they being gangedtogether in actual assembly and indicated at numeral 78. The system isto be considered as in use by adiver, i.e. dynamic, during which theoxygen supply is depleted according to his requirements.

Each of the electrolytic oxygen sensing cells 208, 215 and 222 provide acurrent flow directly related to the concentration of oxygen in thegaseous mixture within the part of the breathing apparatus in which theyhave been incorporated. The currents provided by the electrolytic oxygensensing cells 208, 215 and 222 flow through thermistors 207, 214 and221, respectivey, causing a voltage drop across each one.

The direct voltage, which is proportional to the concentration of oxygenas sensed at stage 200 appearing across thermistor 207 is fed to theinput terminal of signal processing amplifier 225 via lead 211, andappears across capacitor 231 connected to the positive terminal 230 ofoperational amplifier 228. An amplified output, from directly coupledoperational amplifier 228, appears at point A and is directly linearlyrelated to its input. The output from point A is fed via resistor 238 tomicroammeter 239 on which the percentage of deflection indicates theconcentration of oxygen, i.e., zero to 2 atmosphere, as sensed byelectrode arrangement 208.

As will be understood, the voltage outputs arising at stagesZOl and 202are processed identically to that of stage 200 and are fed to theirrespective microammeters 256 and 258. Thus, three independent amplifiedvoltages directly related to oxygen partial pressure appear at points A,A and A.

The amplified positive output voltage from operational amplifier 228,appearing at point A, is coupled to point EL So long as the voltage atpoint E remains within the range of from approximately l.9 voltspositive to approximately 3.3 volts positive corresponding to sensedoxygen partial pressure of about 0.4 atmospheres to about 0.7atmosphere, the voltage at point A effectively appears at point E.

Referring to the voltages at points E and E", the signals incoming toprocessing amplifiers 226 and 227 are processed identically to theforegoing voltage appearanceat point B. Therefore, they need not beindividually discussed.

Normal functioning of the apparatus in use by the diver results involtages well above 1.9 at points E, E and El, usually only slightlyabove 2.4V but not above about 3.3V, and such voltages are processedthru opera 'tional amplifier 243 and thereafter in a manner hereinafterdescribed to operate the oxygen input solenoid valve and effect thereplenishment of oxygen in the system in proportion to the loweredvoltage inputs following oxygen usage by the diver. Of course, normalfunctioning is expected, it is intended, and it is the usual in thecourse of using the equipment. However the aspect of some abnormality ina system of this, or any type, whereby the diver is endangered, is ofparamount interest herein. Since the final processing thru point D tothe solenoid valve is discussed at a later point, and such processing isthe same whether or not the input is normal, discussion of variationsfrom normal voltages at points E, E and E" is presented below. inrelation to the other important circuitry. Moreover, a very greatamountof repetition will be possible tot avoid, and better understanding ofthe circuitry will be i had, by a discussion of such variations at thispoint together with their possible interpreted meaning by the diver inobserving the indicators.

In the event either one or more of the voltages appearing at points E, Eand E" are below or above the established range of about 1.9v to about3.3V, the circuitry functions to hold the voltage at the limiting value.If only one signal voltage reaches the clipping point the remaining twocontinue to operate the system If two or all signal voltages shouldreach the clippingpoint, the system will not operate but the meters maystill be used as indicators for manual control so long as two continueto read similarly. The reason (or reasons) for the occurrence is indeedimportant to the diver but, herein such are not necessarily so much amatter of concern; moreover, discussion of all causal possibilities indetail would be very extensive and also is not considered to benecessary. However, for example, the cause may be a malfunction of thesolenoid valve such that it is on open position full time, or on closedposition full time, or batteries may be failing. If it is either,switching to the reserve batteries may restore normal operation;however, if the reserve batteries do not do so, immediate surfacingprocedure is undertaken. Since the helium supply is 10 percent oxygen,it may be employed according to known techniques from maximum depth ofthe dive as the oxygen supply. The helium supply may be employed at anyless depth; but if in shallow water, e.g. 60 feet or less, damage ordanger is not likely from as much as 3.0 atmospheres oxygen for thecorresponding short surfacing time. Therefore, the diver is not inserious trouble even if oxygen is fed in via the by-pass line describedhereinbefore and surfacing is gotten under 'way according topredetermined and diver-learned procedure. Additionally, if the problemis only in the solenoid valve, its oxygen supply may be cut off, andoxygen then fed via the by-pass line manually, in which case thecircuitry will serve to supply concentration indications.

Since fresh operational long life and similar reserve batteries arealway employed as a precaution, especially in deep dives, for example,200 feet and deeper, and/or if the time for operations at such depths isnot long, batteries are not likely to cause an emergency. Similarly, amalfunction'in high quality solenoid valve equipment is most unusual ifit is. properly maintained, for example, free of dirt. Accordingly,unless the equipment is seriously damaged so as to sever electricalleads or bring about a total short circuit, all of the voltagesappearing at points E, E and E" are not likely to fall outside theintended range. One voltage might, however, (though not very likely) dueto many causes. Such an outside voltage may be termed spurious and istreated herein in the main without regard to cause. The important pointto be noted is that by the clipping of a spurious signal, in theparticular system here described, the system continues to functionnormally although the diver has been warned by the alarm and will havenoted his microammeter oxygen indicators and unless it be quitedesirable not to do so, he will begin surfacing at once. If it be quitedesirable to remain submerged for a time at the working depth, theoxygen indicators supply him with intelligence from which he can make adecision in reasonable safety and with knowledge in any event that anemergency exists and that he must proceed, if at all, with due cautionand attention to his system, and his physiological reactions. His buddydiver, .of course, will have been alerted.

if in observing the oxygen indicators two are indicat-. ing nearlyidentically, whereas one is at odds, it will be most reasonable on thebasis of statistical probability as hereinbefore explained to make theassumption that the one is faulty since it is not likely that one hascorrectly sensed a real danger and warned of it while two havemalfunctioned in the same way at the same time because of some unrelatedinternal fault. (As hereinbefore indicated, it is proposed as an adjunctto this invention, and as a part thereof, that a special entirelyseparate oxygen concentration testing instrument be supplied for probingthe internal oxygen system so that its measurement may be compared withthe indicators of the main system, whereby substantially absolutecertainty is afforded. Such an instrument will be obvious as to mannerof construction following the teachings herein.)

From the foregoing it will be appreciated that an enormous number ofdifferent operational occurrence might be described in which the presentequipment is useable. Yet, its function insofar as voltage clipping andaveraging is the same. It is for the plurality of sources of informationin any case invaluable to the diver, the preservation of extendedoperability notwithstanding the statistical failure aspect of oxygenconcentration control systems, irrespective of cause or type of failure,and the very high probability of safety from oxygen poisoning or anoxiafor which the invention is especially notable.

Thus, returning to the circuitry (which should now be more readilyappreciated as a whole and in relation to the diver,) the signalclipping at all of points E, E and E or any one or two of them occurselectronically in the same manner via their respective circuitry, atwhich time the alarm circuitry is also energized. A discussion of themanner of operation of this voltage clipping circuitry is presentedbelow. A discussion relative to the point E only is provided since thecorresponding similar circuitry functions in the same manner.

In the event the voltages at point B falls to about 1.9 volts positiveindicating either-an oxygen partial pressure of approximately 0.4atmosphere or some mal-occurrence in the system, base-emitter currentflows in normally nonconductive transistor 247 holding point E at apotential of 1.9 volts positive because of the connection of the baseelectrode 256 to the positive 2.4 volt terminal 294 of the regulatedpower supply 295. When transistor 247 conducts, its emitter-collectorcurrent flows through resistor 249 which lowers the voltage at point Bcausing normally nonconductive transistor 279 to conduct. Theemitter-collector current of transistor 279 flows through and activatesaudible alarm device 281. In the event the voltage at point E rises toabout 3.3 volts (07 atm.) positive, similarly indicating either excessoxygen concentration or a maloccurrence, current flows through diode 250and baseemitter path of normally nonconductive transistor 252 holdingpoint E at a potential of 3.3 volts positive because of the connectionof the base electrode 255 to the positive 2.4 -volt terminal 294 of theregulated power supply 295. Transistor 252 conducts; itsemittercollector current flows through resistor 254 which raises thevoltage at point C causing normally nonconductive transistor 291 toconduct. The emitter-collector current of transistor 291 flows throughresistor 288 lowering the voltage on collector 290, causing normallynonconductive transistor 285 to conduct. The emittercollector current oftransistor 286 flows through and activates audible alarm device 281.

As can be seen from the foregoing a processed voltage signal appears atpoint E whichmay range from about a positive 1.9 volts (representing apartial pressure of about 0.4 atmospheres) to about positive 3.3 volts(representing a partial pressure of about 0.7 atmosphere). Thus, withinthe range mentioned above, is a possible signal of positive 2.4 voltswhich represents a partial pressure of about 0.5 atmosphere.

The discussion which now follows refers to the final processing of thethree signals thru the averaging amplifier to the solenoid.

The processed voltage signal appearing at point E is coupled throughresistor 241 to the negative input terminal 242 of averaging amplifier243'which is an operational amplifier. Similarly processed voltagesignals,

which are developed in signal processing amplifiers 226 and 227 andappear at point E and E" are coupled via resistors 259 and 260,respectively, to the negative input terminal 242 of averaging amplifier243. Since resistors 241, 259 and 260 are the same size, .the threeprocessed signals are effectively averaged, and the average signalappears on the negative input terminal of averaging amplifier 243. Whenany one of points E, E or E, is being held at a constant positive 1.9 to3.3 volts because of the operation of the clipping stages forming partof respective signal processing amplifiers 225, 226 and 227, only theprocessed signals appearing at the point or points which are not clippedwill contribute to the changing of the output from averaging amplifier243. The clipped signal will, of course, pull the average slightly fromthe-correct value but this effect is small and of no consequencephysiologically.

Whenever the average signal appearing on the negative input terminal 242of averaging amplifier 243 passes below the selected control point of2.4 volts, the output from averaging amplifier 243 appearing at point Dreverses from extreme negative to positive. As the output at point Dpasses through zero and becomes positive, transistor 263 conductslowering the voltage on its collector 265 causing transistor 269 tobecome conductive. When transistor 269 conducts, its emittercollectorcurrent flows through the oxygen control solenoid valve 40 whereby it isopened. Additional oxygen is supplied to the breathing apparatus untilthe average signal appearing on the negative input terminal I242 ofaveraging amplifier 243 increases above 2.4 volts positive. The outputfrom averaging amplifier 243 appearing at point D reverses from extremepositive to negative. As the output at point D passes through zero andbecomes negative, and transistor 263 becomes nonconductive, the voltageon its collector 265 rises causing transistor 269 to becomenonconductive thereby interrupting current flow in solenoid 40 allowingthe oxygen supply valve to close. The cycle is constantly repeated, andadditional oxygen supplied as needed to maintain the concentration ofoxygen in the breathing apparatus at a partial pressure near 0.5 atmosphere.

Referring again to matter of preventing signal strength from risingabove or falling below certain fixed limits, herein referred to asclipping, it may be helpful to discuss the reaction of the system to thenew intelligence as such appears in use. Such discussion can hardly bemore than an approximation because it must be understood that the systemis in use, i.e., dynamic, and therefore the example can only be taken asreal in contemplation of the system becoming static until its reactionis complete.

As aforesaid the three voltage sources are averaged. The average inputin use, and-being processed thru to point D and the solenoid 40, isabout 2.4 volts or slightly higher. If the signal of one sensor weregradually falling due to some malfunction, the oxygen concentrationwould rise due to the higher signal values required of the remaining twocorrectly functioning sensors in order to maintain the said 2.4 voltaverage.

Oxygen concentraiton would continue to rise until the erroneous signalwas clipped at about 1.9 volts at which the oxygen concentrationrequired to produce the signal strength needed from the correctlyfunctioning sensors to hold the average would be about 0.53 at-.mosphere. Conversely, if a malfunctioning sensor were producing arising signal the oxygen concentration would drop until clipping of theerroneous signal occurred at about 3.3 volts, resulting in an oxygenconcentraion of about 0.41 atmosphere.

It is thought that the manner of using the described embodiment of theinvention will be quite apparent to those skilled in the art; however,by way of assistance the following procedure is set forth which has beenfound to be satisfactory.

Considering, for example, a dive of 300 feet, the oxygen supply tankshould be pressured to approximately 2,250 lbs. The inert gas tank,preferably helium and oxygen should be at a similar pressure. The carbondioxide removing material should be fresh. Preferably, all batteriesshould be replaced. The sensors are supplied with about 2 drops, 1Nsolution of potassium hydroxide and the membrane should then bepositioned securely against potassium hydroxide loss in use. Obviously,the membrane should be free of grease etc., and undamaged. A Teflon orpolyethylene membrane of about one mil thickness isfound to be suitable.Thdy are then secured in their holding base. i

The valve orifice constituting part of the solenoid valve should beadjusted so as to avoid blasting. In normal use it has been found to beadvantageous that the oxygen be pulsed into the system for about 3seconds every to seconds. This intermittent flow will bi: seen to reducebattery drain. The electric switch ii; turned on and calibration of theinstrument is completed as heretofore described.

The parts are then assembled, care being takej against leakage.

There then being only 20 percent oxygen operatin the system, the alarmcircuitry will be sounding.

With the mouthpiece in place, the equipment is taken into the water to adepth of a few feet and the main oxygen supply valve leading to thesolenoid valve l is turned on whereby the wanted oxygen begins to flowinto the system. The helium valve is then opened to start pressureequalization. With the pressure equalized l the system will come toapproximately 0.5 atm. oxygen partial pressure under normal breathingwithin about 30-40 seconds. As the descent is thereafter continued tothe established depth, helium is constantly fed in as needed to balancethe pressure. The systemshould be closely observed for any sign offault.

It will be appreciated that those utilizing the device of this inventionwill need to become thoroughly experienced with it, at which time theymay choose different courses of action in circumstances where one ormore of the indicators show oxygen partial pressure outside theestablished range. Until such experience is gained, and preferablythereafter, of course, if a warning signal is heard or one or moremeters show outside the range, the dive should be aborted at once. inany event, cause for alarm should be the signal to switch to reservebatteries, and, even though such batteries restore normal conditons, thedive should be aborted, since obviously the reserve batteries may causea similar result; however, so long as the reserve batteries provideproper operation of the system, the system may be utilized in reachingthe surface.

Some observations from experience in use may be helpful. Should theindicators by any chance shown oxygen at a too high level, for example,indicating close to the top end of the range or above, it may be thatthe bypass oxygen line is pouring oxygen into the system at a very highrate. Accordingly, it should be checked to as sure that it is closed. Ifthe valve is not open, the main oxygen supply should be cut off and thesystem exhausted of gas content by compressing the breathing bag. Returnto the surface should then be by way of valving in the helium supplywhich contains 10 percent oxygen (although this may be varied) and willsupport the needs of the diver during the ascent. ln feeding in thehelium-oxygen supply, the bag should be reinflated and the gas breatheduntil the meters show about 40, meaning an oxygen partial pressure ofabout 0.4 atm. The helium mixture should be resupplied in cycles, whichshould occur under normal breathing about every 30 to 40 seconds orreplinished with oxygen by opening the tank valve and bleeding in oxygenusing the meter as a guide.

Should it occur that all meters read too low, the probability is thatthe solenoid valve is not working. Oxygen is of course then valved inmanually, the content being monitored by the partial pressureindicators.

Should all meters read zero it is apparent that the circuitry isinactive, and that the meters cannot be employed for monitoring oxygen.In such case, the helium supply is relied upon as above described. Itgoes ,without saying that the dive program should never leave the diverwith less useable oxygen than required for his safe return to thesurface regardless of other considerations. Calculations in this regardare well known to those skilled in the art and need not be describedherein.

While embodiments of an electronic control apparatus of the presentinvention have been described in detail, other embodiments and numerousmodifications are contemplated as being within the invention, and thescope and spirit of the claims herein.

Having described a system involving three monitoring stages, it isdesired to point out that any desired number of monitor stages may besimilarly employed. It is again pointed out that three such stagesprovide significant advantages over a single stage or two stages,especially when employed in relation to clipping circuitry, as hereindescribed, or similarly effectivemeans for nullifying or otherwiseeliminating an unwanted signal. It is further pointed out that clippingas herein described is not mandatory provided other means are includedin the circuitry for elimination or nullification of an unwanted signal,such means being compatible with requirements of the oxygen input means,including its actuating circuitry. For example, means may be providedeven for manual switching when the alarm sounds in order to void anunwanted signal in a three signal system.

Among the possible other embodiments, are embodiments in which theaveraged signal, developed from the plurality of processed signals fromthe plurality of signal-processing amplifiers, is directly utilized tocontrol a switching device for the, valve controlling solenoid or thelike, thus, replacing the operational amplifier; however, such amplifieris highly desirable because of the steepness of slope at the zerocross-over point and the simplicity of circuitry by which such slope isprovided. Obviously the averaging amplifier may be replaced by amultivibrator.

Thus, as applied to diver breathing apparatus and similar applications,the invention extends more broadly to the provision of plural means fordelivering a corresponding number of signals proportional to oxygenconcentration, and means for combining said signals and thereafteremploying the resulting combined signal to operate oxygen supply meansin a manner to supply oxygen according to predetermined concentration,there also preferably being associated means for indicating the oxygenconcentration represented by each such signals and/or relevant sensi--ble alarm means. However, where the invention is applied in situationsinvolving the control of the environment relative to material ratherthan human or animal life, the indicator-alarm provision may be replacedby operation stopping means, or such may be an added feature togetherwith the indicator and/or alarm feature. Thus, for example, where achemical process is .under automatic gas control the system may beemployed to effect control while guarding against a dangerouslyexplosive mixture. From this it will be apparent. that the invention isnot limited to the control of an oxygen environment; rather it isapplicable to a wide variety of operations where a condition, e.g., anitrogen atmosphere, is critical or a temperature range is critical, thesensing means being replaced by a means responsive to the condition.Additionally, the invention may be employed to monitor a fluid andcontrol a condition therein, for example, an oxygen-containingbreathable liquid.

Still more narrowly however, and as applied to oxygen concentration orotherwise, the invention preferably includes means which may be plural,for eliminating, or effectively nullifying, one or more unwantedsignals, while still leaving the oxygen supply means operable to supplyoxygen within a safely breathable range related to the usersenvironments or changing environment as such may be following signalrejection, such means preferably being electrical. Moreover, such meansmay be or involve alternate circuitry relative and responsive to themodified signal for operating the input means.

Further, it is pointed out that any suitable type of oxygen sensing ormonitoring device may be employed;

' and that different types, or modifications of the same type of such,may be employed within the same operating unit. Additionally, differenttypes, or modified types may be employed in the same unit, they being ofsuitable reliability, thereby affording assurance against the occurrenceof plural simultaneous failure or fault dueto a common cause or inherentcharacteristic. Thus, similarly reserve batteries may be from a sourcedifferent from those in operation, or they may be from a different lot.

Further, it is remarked that the range for oxygen concentration (0.4-0.7atmosphere) is regarded as particularly suitable for use under theconditions described herein, especially in relation to the diverbreathing equipment; however, such is revealing of the potential of thesystem rather than limiting upon the invention. The range and thecontrol point could, of course, be made variable by means obvious tothose skilled in the art. Moreover, the desired concentration may berelated and controlled according to any suitable voltage level.Additionally, the invention herein does not require that the oxygenlevel be held constantly near 0.5 atmosphere; rather, while such isdesirable in the described embodiment, deviation therefrom may besubstantial, and then replenishment, may take place, such permitting,for example, the use of equipment involving a slower response to oxygendepletion and/or the applied signal.

The expression signal failure" is used in the claims hereinafterpresented in a broad sense, and it is intended to refer to all possiblevariations of signal value from the normal gas concentrationproportional value, including the absence of a signal as would result,for example, from a dead sensor. The term spurious refers to a signalwhich is erroneous, either at a fixed or changing value, in relation togas concentration. As will be understood a spurious signal may degradeto the point of complete absence of a signal. In the course of such,however, it will have been limited in effect by the clipping circuitry.

What is claimed is:

I l. A device for maintaining the concentration of a lgas within a zoneat or near a predetermiend desired llevel, which device comprises atleast three separate means for sensing the instant gas concentrationexisting in said zone and for producing separate signals normallyproportional thereto, means for receiving said {three signals anddelivering thereupon a combined signal output normally similarlyproportional to said concentration; gas supply control means responsiveto said output and operable to effect adjustment of said gasconcentration in said zone when said output deviates from a valuecorresponding to said desired level; said device also including meansfor controlling the effect of either of said separate signals upon saidoutput in the event of an occurrence leading to a signal failure,whereby said output continues to be compatible with the operationalcharacteristics of said gas supply control means and said concentrationis maintained substantially as normal notwithstanding such occurrence.

2. A device as claimed in claim 1 wherein said combined signal is anaverage of said three or more signals.

3. A device as in claim 2 wherein said controlling means is clippingcircuitry adapted to limit the signal effect upon said output at apredetermined signal value or values related to preselected gasconcentration.

4. A device as claimed in claim 3 wherein said value or valuesconstitute end limits for a range of signal values embracing thatcorresponding to said desired concentration level.

- 5. A device as claimed in claim 4 wherein the end limits of the signalvalues at which clipping occurs are established so as to providetolerable gas concentration as effected by an average signal outputfalling with range of values.

6. A device as claimed in claim 5 wherein said range of values isrelated to that value corresponding to said desired level such that aspurious signal contribution to said output or a signal contribution tosaid output following clipping of a spurious signal is compensated forby remaining normal signals and said output remains within said range ofvalues.

7. A device as claimed in claim 6 wherein indicator means is providedfor each of said proportional signals.

8. A device as claimed in claim 7 wherein warning means is provided togive notice of signal failure.

said

9. A device as claimed in claim 6 wherein warning means is provided togive notice of signal failure.

10. A device as claimed in claim wherein indicator means is provided foreach of said proportional signals.

1 l. A device as claimed in claim 10 wherein warning means is providedto give notice of signal failure.

12. A device as claimedin claim 5 wherein warning means is provided togive notice of signal failure.

13. A device as claimed in claim 4 wherein indicator means is providedfor each of said proportional signals.

14. A device as claimed in claim 13 wherein warning means is provided togive notice of signal failure.

15. A device as claimed in claim 4 wherein warning means is provided togive notice of signal failure.

16. A device as claimed in claim 3 wherein indicator means is providedfor each of said proportional signals.

17. A device as claimed in claim 16 wherein warning 22. A device asclaimed in claim I wherein indicator means is provided for each of saidproportional signals.

23. A device as claimed in claim 22 wherein warning means is provided togive notice of signal failure.

24. A deviceas claimed in claim 1 wherein warning means is provided togive notice of signal failure.

* IF =l= i

1. A device for maintaining the concentration of a gas within a zone ator near a predetermiend desired level, which device comprises at leastthree separate means for sensing the instant gas concentration existingin said zone and for producing separate signals normally proportionalthereto, means for receiving said three signals and delivering thereupona combined signal output normally similarly proportional to saidconcentration; gas supply control means responsive to said output andoperable to effect adjustment of said gas concentration in said zonewhen said output deviates from a value corresponding to said desiredlevel; said device also including means for controlling the effect ofeither of said separate signals upon said output in the event of anoccurrence leading to a signal failure, whereby said output continues tobe compatible with the operational characteristics of said gas supplycontrol means and said concentration is maintained substantially asnormal notwithstanding such occurrence.
 2. A device as claimed in claim1 wherein said combined signal is an average of said three or moresignals.
 3. A device as in claim 2 wherein said controlling means isclipping circuitry adapted to limit the signal effect upon said outputat a predetermined signal value or values related to preselected gasconcentration.
 4. A device as claimed in claim 3 wherein said value orvalues constitute end limits for a range of signal values embracing thatcorresponding to said desired concentration level.
 5. A device asclaimed in claim 4 wherein the end limits of the signal values at whichclipping occurs are established so as to provide tolerable gasconcentration as effected by an average signal output falling with saidrange of values.
 6. A device as claimed in claim 5 wherein said range ofvalues is related to that value corresponding to said desired level suchthat a spurious signal contribution to said output or a signalcontribution to said output following clipping of a spurious signal iscompensated for by remaining normal signals and said output remainswithin said range of values.
 7. A device as claimed in claim 6 whereinindicator means is provided for each of said proportional signals.
 8. Adevice as claimed in claim 7 wherein warning means is provided to givenotice of signal failure.
 9. A device as claimed in claim 6 whereinwarning means is provided to give notice of signal failure.
 10. A deviceas claimed in claim 5 wherein indicator means is provided for each ofsaid proportional signals.
 11. A device as claimed in claim 10 whereinwarning means is provided to give notice of signal failure.
 12. A deviceas claimed in claim 5 wherein warning means is provided to give noticeof signal failure.
 13. A device as claimed in claim 4 wherein indicatormeans is provided for each of said proportional signals.
 14. A device asclaimed in claim 13 wherein warning means is provided to give notice ofsignal failure.
 15. A device as claimed in claim 4 wherein warning meansis provided to give notice of signal failure.
 16. A device as claimed inclaim 3 wherein indicator means is provided for each of saidproportional signals.
 17. A device as claimed in claim 16 whereinwarning means is provided to give notice of signal failure.
 18. A deviceas claimed in claim 3 wherein warning means is provided to give noticeof signal failure.
 19. A device as claimed in claim 2 wherein indicatormeans is provided for each of said proportional signals.
 20. A device asclaimed in claim 19 wherein warning means is provided to give notice ofsignal failure.
 21. A device as claimed in claim 2 wherein warning meansis provided to give notice of signal failure.
 22. A device as claimed inclaim 1 wherein indicator means is provided for each of saidproportional signals.
 23. A device as claimed in claim 22 whereinwarning means is provided to give notice of signal failure.
 24. A deviceas claimed in claim 1 wherein warning means is provided to give noticeof signal failure.